Tumour development at its early stages is usually accompanied by membrane breakdown and bleeding. Therefore, one of the first warnings of cancer in the gastrointestinal tract is blood lost into the stool. Methods have been developed to identify even microscopic amount of blood in feces by occult blood tests as outlined for example by Kutter et al. in Dtsch. Med. Wschr. 99(1974)2332. Such fecal occult blood tests enable to receive indication of tumoural development in its earliest stages, much before the patient has any complaints. This occult blood test in feces is an important tool for screening cancer in the gastrointestinal tract, i.e., the test identifies an attribute that may be linked to cancer in the gastrointestinal tract. However, such test does not give any indication as to the location of the bleeding. Furthermore, the presence of fecal blood may also result from non-cancerous conditions. Therefore, when bleeding is detected in feces, further diagnostic test must be carried out on the patient in order to identify the location and nature of the bleeding.
The diagnostic aids for the identification of the source of bleeding in the gastrointestinal tract which are most commonly used clinically are: gastroscopy, sigmoidoscopy, colonoscopy, duedenoscopy, selective abdominal angiography, double contrast barium anema, X-ray with contrasting material such as barium sulfide and ultrasonic imaging. The detection by all the above mentioned diagnostic aids is based on visualizing the bleeding lesion. Consequently, when the location of such lesion is detected an appropriate treatment can be chosen. Since surgical resection is the major mode of treatment for gastrointestinal tumours, it is of outmost importance to diagnose and localize gastrointestinal tumours at their earliest stage of development.
Unfortunately, in about 20 percent of the patients in which the occult blood test is positive, the location of bleeding by any of the above mentioned known diagnostic aids cannot be established. Some of the non diagnosed cases are accounted for by non-tumoural bleeding which will disappear after a lapse of time. However, other cases are due to tumoural bleeding in its earliest stages, while the small erosion of the membrane and the small amount of bleeding can not be viewed by any of the known diagnostic methods. Moreover, it is also known that in some cases of severe bleeding of the gastrointestinal tract, none of the known diagnostic aids detect the location of the bleeding due to obscureness. As a result, patients are sometimes taken to the operating table before a complete diagnosis has taken place for exploration inside and surgical resection is effected on organs suspected as being the source of bleeding, before complete confirmation of the localization of bleeding has been effected.